Preparation, structure and hydrothermal stability of alternative (sodium silicate-free) geopolymers

• Published in: Journal of materials science Vol. 42; no. 22; pp. 9267 - 9275
• Main Authors: KOLOUSEK, David, BRUS, Jiri, URBANOVA, Martina, ANDERTOVA, Jana, HULINSKY, Vaclav, VOREL, Jindrich
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.11.2007; Springer Nature B.V
• Subjects: Activation; Applied sciences; Chemical composition; Composites; Ecology; Exact sciences and technology; Forms of application and semi-finished materials; Geopolymers; Hydrothermal treatment; Hydroxides; Inversions; Kaolin; Materials science; Mechanical properties; Mineralogy; Moisture content; NMR spectroscopy; Organic chemistry; Polymer industry, paints, wood; Sodium; Sodium silicates; Solidification; Stability; Structural analysis; Structural stability; Technology of polymers; X ray powder diffraction; X-ray diffraction; Zeolites; Clay; Aluminum polymer; Thermal ageing; Preparation; Mechanical properties; Zeolite; Experimental study; Kaolin; Inorganic polymer; Silicon polymer; Calcining
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-007-1910-5

In this contribution, we present the preparation and structural characterization of a new type of alternative (sodium silicate-free) geopolymer system. A new procedure of geopolymer synthesis based on the preparation of a reactive geopolymer precursor by direct calcinations of low-quality kaolin with Na/K hydroxides is introduced. The subsequent formation of geopolymer matrix does not require activation by alkaline silicate solution. The compact and hardened material was prepared only by adding a small amount of water. Besides the introduction of a new synthetic procedure, we focused also on the systematic study of chemical structure, mineralogical composition and hydrothermal stability of the prepared geopolymer systems as seen by solid-state NMR spectroscopy and powder X-ray diffraction (XRD). An important part of our contribution is the demonstration of structural and mineralogical changes induced by hydrothermal treatment and long-term aging of the prepared geopolymers. It was found that redistribution of basic structural units (SiO44− and AlO45−) and gradual formation of zeolite fractions can be related to the observed changes in mechanical properties. Up to a certain level, the presence of zeolites enhances the mechanical properties of the prepared geopolymer systems. However, the additional formation of a new generation of zeolite fractions, occurring over the long-term period causes an inversion of this trend and a dramatic reduction of mechanical strength. Nevertheless, formation of the geopolymer matrix by alkaline and thermal activation of low-quality kaolin has the potential to be used in ecological problems solving (solidification of powdered and dangerous waste materials).